Electrical discharge device



1932 L. LANGMUIR ET AL ELECTRICAL DISCHARGE DEVICE Original FiledOct. 1. 1924 E ,y i? w mm/4m E mi mw h %AM ...rrnjm T lmn i vm h .RK T

Patented Dec.'2v, 1932 UNITED STATES PATENT OFFICE IRVING LAN'GMUIR ANDKENNETH H. KINGDON, 0F SCHENEC'IADY, NEW YORK, AS-

SIGNORS 'IO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORKELECTRICAL DISCHARGE DEVICE This application is a continuation in partof our application filed November 6, 1923, Serial No. 673,165 and onwhich U. S. Patent 1,648,312 was granted November 8, 1927.

The present invention relates to the construction of electricaldischarge devices having in addition to the cathode a plurality ofcooperating electrodes, one which serves as an input or grid electrodewhereby the current in the device is electrostatically controlled.

Heretofore, in the construction of radio detectors, electric amplifiers,oscillators and similar electron devices, the grid commonly has beenconstituted by a wire coil or screen which was interposed between thecathode and a surrounding anode.

In accordance with our invention, we have provided an improved device ofthis character in which the anode as well as the input or grid electrodeconsists of plate-shaped members which are arranged in interleavedrelation with the members of the anode, the members constituting theinput electrode being in closer electrostatic relationship to thecathode than the members constituting the anode. This construction is ofparticular ad vantage in a device containing a cathode sensitive topositive ion bombardment, as the positive ions are attracted to the gridinstead of the cathode.

The novel features of our invention will be set forth with greaterparticularity in the accompanying claims, while details of our inventionwill be described in the following specification taken in connectionwith the accompanying drawing.

In the drawing, Fig. 1 is a side elevation ofa three-electrode amplifiertube embodying our invention; Fig. 4 illustrates in perspective therelation of the grid and anode members, the supports being omitted forthe sake of clearness; Figs. 2 and 3 illustrate a modification, and Fig.5 is a diagram of a radio receiving system} in which a tube embodyingour invention may be employed as a radio detector and amplifier,theelements of the tube-in this figure being shown in horizontalsection. i

Our invention will be described with par- No. 740,998. Renewed October30, 1931.

ticular reference to an electron discharge device containing a substancesuch as caesium or rubidium, which is capable of increasing the electronemission of a thermionic cathode by the formation upon the cathode of anadsorbed film, as described in detail and claimed in our priorapplication Serial No. 673,165, of which this application constitutes acontinuation.

The device shown in Fig. 1 comprises as usual, an exhausted container 1,consisting of glass or other convenient material and containing afilamentary cathode 2, which preferably should have a substantiallyrectilinear extension. The cathode 2 is supported from the leading-inconductors 3 and 4, which are sealed into a stem 5, as usual. Betweenthe leading-in conductor 4 and the end of the cathode remote from thestem 5 is a supporting structure 6, which terminates ina spring 7 inorder to maintain the cathode taut. Provided within the container 1 alsois a quantity of metallic caesium, as indicated at 8. The caesium may beintroduced from a side tube (not shown) containing a mixture of caesiumchloride and calcium which when heated yields caesium.

In these tubes containing alkali metals, care should be taken to avoidcondensation of metal on the stem as such condensation will causeelectrical leakage between wires passing through the stem. Condensationof this kind is particularly apt to occur on those places where caesiumoxide is present. The stem should be freed from condensed caesium byheating, and the parts where caesium has deposited should be cooledsuiticiently to avoid perceptible vapor pressure of caesium when theoxygen is introduced. To reduce electrical leakage, it is advantageousto surround the electrode leads with short glass tubes spaced away fromthe leads as shown in both figures of the drawing. (See .10, Fig. 1.)

In the prior application above mentioned we have .described particularlythe property of an electron discharge device containing in addition tocaesium or the like a layer of adsorbed material 'on the cathode,preferably an oxygen film which has the property of causing the cathodesurface to more tenaciously hold the caesium bound thereon than would aclean unoxidized cathode surface. While the present invention is not tobe understood as being limited to this particular form of device, wewill describe for the sake of completeness the preparation of the entiredevice, including the oxidation of the cathode surface. Although thedescribed structure has particular advantages in a device having acathode sensitive to positive ion bombardment, it should be understood,of course, that the structure covered by our present application can beused in other forms of discharge devices.

When the cathode is to be provided with an oxygenous layer, the envelopeof the device first is evacuated thoroughly and the filament heated toahigh temperature to free its surface of impurities and to removeoccluded gas. In the case of a tungsten cathode this temperature shouldbe about 2500? Kelvin. Oxygen then is admitted to the container to apressure of about 20 to 30 microns (0.02- 0.030 mm.) the filamentpreferably being heated to a temperature of about 1400 to 1500 K. for afew seconds, which causes the formation of a thin layer of adsorbedoxygen upon the cathode. The remaining oxygen then is pumped out and. aquantity of caesium or rubidium is distilled into the container, whichmay form a condensate on the wall, as shown at 8, as preferably enoughof the metal is introduced to provide a surplus of unevaporated caesiumat any desired operating temperature.

In some cases after the caesium has been introduced an additional amountof oxygen is admitted to oxidize part of the caesium and preferably inaddition to the oxygen about half as much hydrogen (by volume) as theamount of oxygen is introduced and allowed to clean-up. The tube finallyis sealed oif with the exhaust pump operating. After the tube is sealedoff, the cathode should be heated for a few seconds at about 1300 to1500 K. to get rid of deleterious substances on the oxygen layer.

When the device prepared as above described by the admission of gaseousoxygen is operated with the cathode at a temperature of about 900 K.,the bulb as a whole being at a temperature of 30 C. (303 K.) an electronemission from the cathode of the order of about 200 to 300 milliamperesper sq. cm. of surface is obtained. This emission is of the same orderof magnitude as the emission from a tungsten filament operating in avac-' uum in the absence of caesium or similar activating substances ata temperature of about 2500 K., but the energy required is much less.Both the control electrode and the anode in the device shown in thedrawing consist of flat plateshaped members which are roi- 55 diallypositioned with respect to the cathode,

the cathode being axially positioned in the envelope 1. The anodeconsists of set of plates 11, 12, 13 and 14 and the control electrodeconsists of plates 15, 16, 17 and 18. It should be noted that the set ofplates constituting the control electrode are located somewhat moreclosely to the cathode than the anode plates and therefore are in closerelectrostatic relation to the cathode than the anode plates. By thisconstruction the electron current passing during operation from thecathode to the anode can be controlled, so as to secure relatively largechanges of current by small change of the potential of the grid orcontrol electrode plates. As shown in Fig. 1 the control electrodeplates may be somewhat longer than the anode plates, but this is not.essential. The spacing of the anode and grid plates from the cathode mayeasily be chosen to give an amplification constant of about 4.5 to 5.The anode plates are connected to one another as shown in Fig. 1 byrings 19, 20 to prevent displacement, and the control electrode platesare connected together by a single ring 21. The rings 20 and 21aresupported respectively from the stem 5 by the wires 22, 23 and 24, 25.The wires 23 and 24 are continued through the stem and project from theoutside of the device to permit of electrical connection.

In a tube of this construction the positive ions are almost entirelyformed in the space between the anode and control plates and not betweenthe filament and the plates. The ions, therefore, are produced at pointswhere the electric field draws them to the grid, and they are thusprevented from striking the cathode. Moreover, it is evident thatinasmuch as a general movement of the positive ions formed at thesurface of the anode is in a direction substantially normal to thatsurface and toward the grid member, the cathode is shielded from ionbombardment. It is also apparent that while control and anode members offlat form and positioned in the plane of the filament lend themselvesparticularly well from the manufacture, assembly and operationstandpoint for the purposes stated, it is to be understood that ourinvention is not limited to electrodes of this configuration andarrangement, since the electrodes may take any suitable shape,individually or as a whole, and may be positioned in any relation withrespect to the cathode and with respect to one another as will cause theelectrostatic lines of force between the control and anode members to bedirected substantially away from the filament without departing from ourinvention. These respective electrodes are connected by the usualsealed-in conductors, the cathode conductors being numbered 3 and-4, theinput conductor 24 and the anode conductor 23. For the sake ofsimplicity no base has been shown for the device. This device may beused as a radio detector or as anamplifie'r, with the usual circuitconnections for three electrode devices. For example, in Fig. 5 atypical receiving circuit has been'shown connected to receive signalsfrom the antenna 27. The secondary of the antenna transformer 28 isconnected by the conductor 29 to the plate circuit 23 of the device andby the conductor 24 to the grid electrode 30. The plate circuit containsa source of ourrent 31 and a telephone receiver 32. A tuning condenser33 is provided as usual. When the device is to be used as a detector agrid condenser 34. and a grid leak 35 also may be provided.

The device shown in Fig. 2 closely resembles the device of Fig. 1. Theanode and grid plates in this case are bent substantially at rightangles at one edge to give them greater rigidity and to permit them tobe more readily welded or otherwise attached to the holders. As shown inthis figure two sets of binding rings, or holders, are applied to eachset of electrodes. welded to the rings 36, 37 and the grid plates to therings 38, 39. The cathode 40 in this modification consists of a spiralstretched out to the desired length. By the use of a spiral a greaterlength of wire may be introduced for a given length of electrodes, thusminimizing the cooling efiect of the leads which is especially importantbecause of the low cathode temperatures used.

What we claim as new and desire to secure by Letters Patent of theUnited States, is,--

1. An electric discharge device comprising a container, anelectron-emitting cathode having a generally rectilinear extension, anda plurality of cooperating electrodes each of which consists of groupsof members having a maximum surface extension in a radial direction withrespect to said cathode, each of the respective'members of one groupbeing located respectively between members of the other group, and oneof said groups being in closer electrostatic relationship to saidcathode than the other group.

2. An electric discharge device comprising a container, a cathodetherein having a generally rectilinear extension, an anode and an inputelectrode, said anode and input electrode each comprising a plurality ofsubstan tially fiat members mounted radially about said cathode, themembers constituting the input electrode being in interleaved relationwith said anode members and bei closer to said cathode than said anodemem ers.

3. An electric discharge device comprising a container, a rectilinearfilamentary cathode consisting of refractory material, an anode and anelectrostatic input electrode, said anode and in ut electrode eachcomprising a plurality o flat plates, means supporting said platessubstantially radially with respect to said cathode, the platesconstltuting one of The anode plates aresaid electrodes bein interleavedwith the plates constituting t e other electrode and theplates-constituting the input electrode being closer to the cathode thanthe plates constituting the anode. Y

4. An electric discharge device comprising a container, anelectron-emitting cathode havi a generally rectilinear extension, 9.plurallty of cooperating electrodes in said containers each of whichconsists of plateshaped members mounted radially with respect to saidcathode, the plate members of one electrode being mounted in interleavedrelation with the plate members of the cooperating electrode, each platebeing substantially in the plane which includes said electron emittingcathode.

5. An electric discharge device comprising a filamentary cathode havinga mainly linear extension, 2. grid electrode comprising plates mountedradially about said cathode, each of said plates being respectivelylocated in a plane which. includes the cathode, and an anode electrodealso comprising plates spaced in interleaved relation to said gridplates.

6. An electric discharge device comprising a cathode, an anode and agrid, said cathode having a generally rectilinear extension, said anodeand grid each comprising a group of substantially flat members mountedradially about the cathode and in overlapping relation with one another.

7. An electric discharge device comprising a cathode, an anode and agrid, said cathode having a generally rectilinear extension, said anodean substantially flat members mounted radially about the cathode, eachof the members being located'respectively in a plane which includes thecathode.

8. An electric discharge device comprising a cathode, an anode and agrid, said cathode having a generally rectilinear extension, said anodeand grid each comprising a group of substantially flat plates mountedradially about the cathode and in overlapping relation with one another,each of the plates of one group being located respectively betweenplates of the other group and each plate being located respectively in aplane which includesthe cathode.

9. An electric discharge device including grid each comprising a. groupof o a cathode, an anode and a grid, the anode and grid comprisingsubstantially flat members radially disposed with respect to thecathode, the grid members being closer to the cathode than the platemembers whereby the cathode may be shielded from positive ionbombardment.

10. An electric discharge device including a cathode, an anode and agrid, the anode and grid comprising substantially flat members angularlydisposed with respect to one another, the grid members being closer tothe cathode than the late members whereby the cathode may be s ieldedfrom positive ion bombardment.

11. An electric discharge device including a cathode, a anode and agrid, the cathode having a mainly linear extension and the anode andgrid comprising substantially flat members angularly dis osed withrespect to one another, the cath e being located substantially at the aex of the an le formed by the anode and gri members and the grid andanode being unequally spaced from the cathode.

12. A thermionic valve comprising an anode element and modulatingelements mounted on opposite sides of the anode element, and in spacedrelation therewith, and an electron emitting element located in theplane of the anode element and equi-distant from the modulatingelements.

13. A thermionic valve comprisin an electron emitting element, a seriesof at anode plates, and a series of fiat modulating plates, said anodeplates and modulating plates being alternately mounted in intersectingplanes common to the electron emitting element.

14. A thermionic valve comprising an elee tron emittin element, and twosubstantially flat spaced p ates located substantially parallel with thestream of emitted electrons, and formed therebetween a passageway forthe electronic emission, said electron emitting element being located ina plane bisecting said intermediate passageway.

15. An electron discharge device comprising a container having mountedtherewithin an electron emission element, and in the plane of andedgewise to said element, a cooperating anode element comprising aplurality of plates, and a control element.

16. An electric discharge device comprising a source of positive ions,an electron emitting cathode, an anode adapted to be ositively chargedand an input electrode a apted to be charged negatively with respect tothe anode, said anode and input electrode including members which liesubstantially in planes subtending an acute angle at the cathode wherebythe positive ions formed in the region between the anode and inputelectrode are attracted toward the input electrode and away from thecathode.

In witness whereof, we have hereunto set our hands this 30th day ofSeptember,

- IRVING LANGMUIR.

KENNETH H. KINGDON.

CERTIFICATE. OF CORRECTION. 5

Patent No. 1,892, 244. December 27, 1932.

IRVINGLANGMUIR, ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 3,line 75, claim" 4, for "containers" read "container"; page 4, line 5,claim 11, for "a" second occurrence read "an"; and line 32, claim 14,for "formed" read "forming"; and that the said Letters Patent should beread with these corrections therein that thesame may conform to therecord of the case in the Patent Office.

Signed and sealed this 21st day of February, A. D. 1933.

M. J. Moore,

(Seal) Acting Commissioner of Patents.

